Class D amp question, you amp techs will know.

[Fan Fret]

I've had my Genzler mg350 head about two years and couldn't be happier. Just curious why it has a cooling fan? I thought class D doesn't generate much heat and it's never got warm to the touch in addition I have a similar wattage stereo class D amp with no fan or vents. So why the fan and vents with Genzler? The other funny thing is the stereo amp weighs 25 pounds and the Genzler is super light. Just curious about this class D stuff.Thanks

Actually you'll find that most Class D bass amps have cooling fans. I've had a few Mesa Subways, all with fans. My Quilter Bass Block has a fan. I don't think I've ever seen a GK without a fan.

 

[agedhorse]

Walter's amps did not need a fan to keep them cool. The package is similar to modern, current Class D amps, and even the older designs that are Class A/B don't need a fan to keep them cool.

Walter's amps needed huge heatsink relative to their rated power because the class AB efficiency is so low. Had he gone with fan cooling, the heatsink size could have been reduced by roughly 50-75%.

It's all about cooling efficiency, and as power density increases, as rated load impedances drop, cooling efficiency becomes more and more critical. At some point, passive cooling just can't keep up (especially on class AB/G/H topologies).

 

[Michedelic]

Something that's popular will have at least one fan.

 

[Jeff Scott]

Walter's amps needed huge heatsink relative to their rated power because the class AB efficiency is so low. Had he gone with fan cooling, the heatsink size could have been reduced by roughly 50-75%.

It's all about cooling efficiency, and as power density increases, as rated load impedances drop, cooling efficiency becomes more and more critical. At some point, passive cooling just can't keep up (especially on class AB/G/H topologies).

I never really thought his heatsink was all that large compared to many other amps I've seen, particularly in the hi-fi area.

 

[agedhorse]

I never really thought his heatsink was all that large compared to many other amps I've seen, particularly in the hi-fi area.

Many hi-fi design's heatsink are for visual and marketing purposes rather than performance.

The heatsink are huge compared with the GBE-1200 (for example), the MI-100 is about 60% smaller than the GBE-1200's heatsink but is rated for less than 10% of it's rated power.

Their speakers tended reasonably for the difference is the efficient, fan cooked design of the GBE. In fact it would be impossible to convection cool the GBE.

 

[logdrum]

The obsession to go fanless lives me winded. Nothing is free in physics. You move speakers with 800 watts RMS at 2 ohms, you will build up heat and you need to move that heat. At gig levels the ratio of the fan Nosie to the SPL of the Program audio is wide. That fan noise is negligible. It's an amplifier not a preamp or pedal.

Acoustic Image are also fanless, but I can tell you that they will go into protect mode sooner than a class D of similar watt rating with a fan. It has happened to me so many time that I knw that the master cannot really be push beyond 2 o'clock unless your gain on the input is low., I actually carry a laptop cooler and stick it on top, I love them but this is one of their limitation. Meanwhile a GK Legacy will perform all summer night with the master almost dimed.

 

[agedhorse]

The 800 watt Subway amps have a fan because the power density, high duty cycle and 2 ohm rated real world operation require it for reliability.

The 350 watt Subway model has a lower power density, same duty cycle but with a 4 ohm rated operation doesn't require a fan. Part of this is also a different modulation scheme than the 800 watt models, which is more efficient but can't scale any higher than 350 watts into 4 ohms.

 

[el murdoque]

I never did, but I burnt the location of the on/off switch in memory just in case loll The power cable wraps around the entire heat sink for storage or traveling. Great head and I still use it occasionally with the Peavey 1820 cab.

A friend of mine used one, and told me his had broken down. I don't know why he had to tell such a blatant lie - these things have been around before humans discovered fire and they will be around when humans have wiped themselves off the face of the planet, made to outlast time itself, but I did not care. I gave him mine, and he was very happy about it and still uses it AFAIK. I bought it in '94, used it heavily for a couple of years, then it ended up in a rehearsal room as a backup.

 

[el murdoque]

Walter's amps did not need a fan to keep them cool. The package is similar to modern, current Class D amps, and even the older designs that are Class A/B don't need a fan to keep them cool.

Yes, because they relied on a massive metal radiator attached to the back of the amp.

The Genzler amp the OP posted about is a lot smaller and supposedly lighter than the Walter Woods designs are.

If you took the heatsink and replaced it with a small fan, you could make the WW amp significantly smaller, but I guess that Mr. Woods decided against moving parts and wanted his amps to have passive cooling, so he never did.

 

[ardgedee]

The obsession to go fanless lives me winded. Nothing is free in physics.

If you play loud gigs, worrying about fan noise is more of a distraction than the noise is.

If you play quietly at home (or, I guess, in quiet public spaces), fan noise can be a legitimate distraction.

I can see where the conflict arises when people would rather have (or can only budget for) one really good rig rather than a collection of situation-specific equipment, so the 800-watt fan-cooled monster they use at rock shows is also their bedroom amp. Not necessarily the right tool for the job but you gotta make do.

 

[Giffro]

A friend of mine used one, and told me his had broken down. I don't know why he had to tell such a blatant lie - these things have been around before humans discovered fire and they will be around when humans have wiped themselves off the face of the planet, made to outlast time itself, but I did not care. I gave him mine, and he was very happy about it and still uses it AFAIK. I bought it in '94, used it heavily for a couple of years, then it ended up in a rehearsal room as a backup.

From memory bought my rig about 1982 and used it into 2000ish before buying a lightweight rig, but the Peavey outfit still works fine...just needs muscles to move it as the cab weighs 122 pounds lolll Bomb-Proof

 

[JimChjones]

This could be a problem back in the day when rack mounting gear was far more common. Guys would NOT read the fine print in the manual and leave empty rack spaces above or below as recommended, so you'd see these crammed racks,

It really ****** me off when companies do that. If your product, amp, server, comms kit, whatever needs the extra space for proper cooling then FFS build it into the box. I'd rather have a 2U device than a supposedly 1U device that actually needs to occupy 2U.

 

[Jeff Scott]

Many hi-fi design's heatsink are for visual and marketing purposes rather than performance.

The heatsink are huge compared with the GBE-1200 (for example), the MI-100 is about 60% smaller than the GBE-1200's heatsink but is rated for less than 10% of it's rated power.

Their speakers tended reasonably for the difference is the efficient, fan cooked design of the GBE. In fact it would be impossible to convection cool the GBE.

I agree regarding visual appeal on hi-end hi-fi power amps; sometimes it's almost comcal just how big many of them are.

My Aragon 2004 is quite the opposite, thankfully. The case is the heatsing with just a piece of aluminum angle to mount the transistors to the bottom of the case. It has never gotten warm during the times I'd crank my stereo (albeit, the amp is only 100 watts @8Ω, 200 watts @ 4Ω). My Maggies are around 5Ω.

Yes, because they relied on a massive metal radiator attached to the back of the amp.

The Genzler amp the OP posted about is a lot smaller and supposedly lighter than the Walter Woods designs are.

If you took the heatsink and replaced it with a small fan, you could make the WW amp significantly smaller, but I guess that Mr. Woods decided against moving parts and wanted his amps to have passive cooling, so he never did.

Walter probably used the heatsink he did because he was designing to make his amps reliable, which they basically were, for the most part. Remember, he was making these compact amps long before the concept became the norm in this century (Walter began building his amps in the latter part of the 1970s).

 

[MrRiff]

Actually you'll find that most Class D bass amps have cooling fans. I've had a few Mesa Subways, all with fans. My Quilter Bass Block has a fan. I don't think I've ever seen a GK without a fan.

You're probably right, what made me wonder is on the other hand most class D high power stereo amps don't have fans but as someone posted they're in larger enclosures with other means of cooling. Also a bass amp is gonna get more punishment and pushed harder than a home a stereo.

 

[agedhorse]

If you play loud gigs, worrying about fan noise is more of a distraction than the noise is.

If you play quietly at home (or, I guess, in quiet public spaces), fan noise can be a legitimate distraction.

I can see where the conflict arises when people would rather have (or can only budget for) one really good rig rather than a collection of situation-specific equipment, so the 800-watt fan-cooled monster they use at rock shows is also their bedroom amp. Not necessarily the right tool for the job but you gotta make do.

There are indeed many lower powered, lower volume applications where fan noise can be problematic. That's (one reason) why the D-350 is fanless.

I agree regarding visual appeal on hi-end hi-fi power amps; sometimes it's almost comcal just how big many of them are.

My Aragon 2004 is quite the opposite, thankfully. The case is the heatsing with just a piece of aluminum angle to mount the transistors to the bottom of the case. It has never gotten warm during the times I'd crank my stereo (albeit, the amp is only 100 watts @8Ω, 200 watts @ 4Ω). My Maggies are around 5Ω.

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Walter probably used the heatsink he did because he was designing to make his amps reliable, which they basically were, for the most part. Remember, he was making these compact amps long before the concept became the norm in this century (Walter began building his amps in the latter part of the 1970s).

There's plenty of radiating area on that case to work for low power, low duty cycle hi-fi applications , especially since it doesn't have to drive 2 ohms at high duty cycle.

Walter made the choice not to fan cool, and the heatsink had to be that big to be reliable. Some manufacturers used fan cooling even back then.

You're probably right, what made me wonder is on the other hand most class D high power stereo amps don't have fans but as someone posted they're in larger enclosures with other means of cooling. Also a bass amp is gonna get more punishment and pushed harder than a home a stereo.

Because they are lower powered, drive much lower duty cycles, and don't generally need to drive 2 ohms loads.

 

[cfortner]

Where we are on the subject:

Why do so many old, but also newer amps have such loud, unregulated fans?

Is it really that difficult to build a good fan control that keeps the noise level of the fan low at temperatures of up to, say 60 degrees on the heat sink and only regulates the speed up if it get warmer? For safety, e.g. for example, a bimetal switch bypasses the control when it gets too hot, because the fan can not longer do it or the outside temperature is too high.

I returned a number of amps due to noisy fans.

 

[agedhorse]

Where we are on the subject:

Why do so many old, but also newer amps have such loud, unregulated fans?

Is it really that difficult to build a good fan control that keeps the noise level of the fan low at temperatures of up to, say 60 degrees on the heat sink and only regulates the speed up if it get warmer? For safety, e.g. for example, a bimetal switch bypasses the control when it gets too hot, because the fan can no longer do it or the outside temperature is too high.

I returned a number of amps due to noisy fans.

Yes, it's a LOT of work to design an effective, quiet, reliable and compact cooling system.

 

[cfortner]

I would pay for it, but the Class D amps aren't noisy at all.